Use quick compiler to generate odex for oat file assistant tests.

This is needed to generate non-PIC odex files, because optimizing
compiler always generates PIC.

Change-Id: Ic77a0faef6b36f13c61607327640e3378a7ee75e
diff --git a/runtime/oat_file_assistant_test.cc b/runtime/oat_file_assistant_test.cc
index 4232b88..443e3a8 100644
--- a/runtime/oat_file_assistant_test.cc
+++ b/runtime/oat_file_assistant_test.cc
@@ -175,6 +175,10 @@
       args.push_back("--compile-pic");
     } else {
       args.push_back("--include-patch-information");
+
+      // We need to use the quick compiler to generate non-PIC code, because
+      // the optimizing compiler always generates PIC.
+      args.push_back("--compiler-backend=Quick");
     }
     args.push_back("--runtime-arg");
     args.push_back("-Xnorelocate");